1. Field of the Invention
The present invention relates to pulse monitors with visual readout, in general, and to a cardiotachometer which performs a comparison between selected heartbeat intervals such that when any plurality of the intervals are within a predetermined percentage of each other, the plurality of intervals are averaged, read out and held in the display until the next update.
2. Description of the Prior Art
Heart rate is the basic parameter used to evaluate and determine the condition of the human body. In carrying out its action, the heart produces three wave complexes, designated as P, QRS, and T, each of which corresponds to a particular electrical event within the heart. It has long been known that the R wave produces the greatest electrical activity, and for this reason the R--R interval has been used as a way of measuring the time between heartbeats. By knowing the time between heartbeats, it is easy to determine the number of beats per minute.
The contraction, or period of contraction, of the heart, is referred to as a systole. It coincides with the interval between first and second heart sounds, during which blood is forced into the aorta and the pulmonary trunk. In the same way the R--R interval may be used as a way of measuring the time between heartbeats, the interval between systoles may be used for the same purpose.
During a systole, the heart contracts and forces blood through the arteries, which respond by expanding. Thus, a systole may be detected by placing an appropriate transducer or sensor against any of the well known pressure points on the human body or in an area where blood flow is occurring.
The transducer may be in the form of a pressure transducer, such as a piezoelectric crystal or a phototransducer in the form of a light emitting diode and a photocell.
There are any number of prior art pulse monitors which detect the R--R interval or the systolic rate, compute the heart rate in beats per minute and, then, display every update as an instantaneous beat-by-beat readout. An undesirable feature of this procedure is that movements of the transducer by the user are not distinguished from actual heart pulses by the transducer and thus a false reading occurs. Another cause of false readings is the detection by the transducer of normal respiratory fluctuation or psychomotor responses. These readings manifest themselves in a constantly changing display.
To avoid such false readings, electronic pulse rate measuring devices have been designed to average the time interval over 4, 8, 10, or 16 beats to get an average heart beat. Each of these averaging techniques has its own drawback. In the case of the 4 beat average, there is still some jumping of the readout. The problem with the 8, 10 or 16 beat average is the long time interval between updates. Probably the most important drawback found in all averaging systems is that any error occurring during the period under consideration is also averaged into the final readout.
There is thus a need for a cardiotachometer or a pulse monitor which produces a continuous update and display, and which is not plagued by the problems of inconsistent readout, and the introduction of error from any source, such as, muscle tremor, poor sensor contact, and inappropriate use, to name a few. The present invention is directed toward filling that need.